Refining of lead



Feb. 8, 1949.

W. T. ISBELL REFINING OF LEAD Filed May 25, l944 75 lieu/1m Pam u Patented Feb. 8, 1949- i "2.461230, I V T 7' 'REFINING E William T. IsbelLLHerculaneum, Md, .ass ignor to J osephiLeadfibmpanygNew York; NCY" .a' corporatiomoFNew York in I ,ApplicatioraMav25, 1944,?Serial No.2 53515265 1'1? imer-presentinvention relates to the removal ot. .zinc;from lead, particularlyifrom lead. which hasmeendsilverized by treatment with .zinc,

In the refining of lead, it is common practice to remove silver'from theleadbythe addition of zinc? :fiorm-s with": the silver a 1 zinc-silver compound substantially insoluble in rlead." saturated with zinc at temperatures of the order of 900 F. However, after removal of the zinc-silver crusts the lead contains from 0.5 to 0.6% of zinc which must be removed for most of the commercial uses of lead.

Until recently it has been the usual practice to remove the remaining zinc from the lead by heating the lead to red heat in an oxidizing atmosphere, whereby the major portion of the zinc together with a substantial portion of lead were oxidized to form a slag or dross which was skimmed off and resmelted to recover the lead content.

It was proposed at an early date to remove the zinc by distillation but this method was found to require a relatively high temperature and a large proportion of the lead volatilized with the zinc at the temperature of distillation.

More recently it has been proposed to remove zinc from lead by treating the molten lead with oxidizing agents such as chlorine or nitrates, or with caustic soda, or with mixtures of caustic soda and nitrates. All of these methods require the use of expensive chemical reagents and the zinc is converted into salts or oxide of reduced value.

I have now found that the disadvantages of the previously proposed methods may be avoided and the zinc content of the lead removed and recovered in the form of metallic zinc with substantially no loss of lead and without the use of either high temperatures or chemical reagents, by subjecting molten lead containing zinc to low pressures. It has been found that at absolute pressures not exceeding about mm. and preferably from 1 mm. to 0.5 mm. of mercury and at temperatures of from 900 F. to 1200 F'., preferably at about 1080 F to 1125 F., the zinc content of the lead volatilizes readily With a relatively small proportion of lead and may be condensed and recovered in metallic form.

I have found it to be particularly desirable to condense the zinc vapors upon a cooled surface positioned relatively close to the free surface of the molten lead under vacuum and to provide means, such as a suitable agitator, for continually circulating the molten lead to the surface exposed to the vacuum. An advantageous apparatus for practicing the new lead refining fClaim. (c1. Tr-rs) process comprisesacontainerfor thei lea'd tolberefined, means forheating'the. container, .a bell member, open at the. lower endhprefrablymi; lastabout fortyi-nches in. depth, andad aptedto be "immersed in-. a',,1ch)arge ofnmolt'en leadLin container, .lmeans for evacuating theminterior of 'f the bell .member. and .means. :for; cooling. upper surface... of the .,bell rmembert :A...suitable form of apparatus is shown by way of example in the accompanying drawing.

In the drawing, I is a kettle of, for example, 120 tons capacity mounted in a furnace setting 2. 3 is a removable vaporizer-condenser comprising a bell 4, in the shape of a truncated inverted hemisphere. The flat top surface of the bell is provided with a water-cooled jacket 5 and a vacuum line 6, leading to a vacuum pump, opens into the interior of the bell just below the top surface. A stirring propeller I mounted in agitator Well 8 is driven by motor 9.

The vaporizer-condenser assembly is carried on a framework It) adapted to be mounted on studs H carried by the furnace setting 2.

The following is a typical example of the operation of the process of the invention.

A charge of about 110 tons of lead containing about 0.5% of zinc is placed in kettle I with the vaporizer-condenser removed, and heated to 1100 F. The lead is skimmed free of dross, and the vaporizer-condenser is put in position as shown in the drawing, and water connections to the cooling jacket are made.' The temperature of the lead normally drops about 50 F. when the vaporizer-condenser assembly is submerged in the charge. When the temperature has been brought back to 1090 F., the stirrer and the vacuum pump are put in operation. The temperature is preferably maintained at about 1090" to 1100 F. and the pressure at about 0.5 mm. of mercury during the dezincing treatment which for a batch of this size requires about seven hours.

After the completion of the vaporization, the stirrer and vacuum pump are stopped, the water and vacuum connections are broken and the vaporizer-condenser is removed from the kettle.

The zinc condenses in a coherent crystalline mass on the underside of the water-cooled top surface of the bell, as indicated at l2, and is readily removed by vibrating the surface. Residual portions of the deposited zinc are removed by scrapmg.

In general, about of the zinc content of the lead is recovered and the lead after treatment contains 0.05% or less of zinc. The recovered metallic zinc is useful in the desilverizing oi further portions of lead.

Any cadmium which may be present in the lead, for example, from the ore or from the zinc used in the desilverizing process, will be eliminated from the lead by the treatment of the invention. vIt is therefore possible, when using the a treatment of the invention, to use zinc having a substantial cadmium content in the desilverizing of lead.

Although the apparatus shown and described for the purpose of illustrating the principles of the invention has been found to be particularly useful, the process of the invention is not limited to any particular form of apparatus but may be practiced in any apparatus capable of subjecting the lead to a vacuum of the order of 10 mm, of

Number 4 subjecting the extended surface to a reduced absolute pressure of not more than about 1 millimeter of mercury, and maintaining an extended water-cooled solid surface adjacent said; extended surface of molten lead.

WILLIAM T. ISBELL.

, I REFERENCESfCITED The following references are of record in-the file of this patent:

-UNITED STATES PATENT Name Date 1,208,237 Thomson Dec. 12, 1916 1,233,652 DeBavay July 17, 1917 1,513,307 Berglund Oct. 28, 1924 1,728,942 Marden Sept. 24, 1929 1,821,643 Jones Sept. 1, 1931 2,206,117 Osborn et-al July 2, 1940 2,239,370 Osborn et al Apr. 22, 1941 2,267,698 Janes Dec. 23, 1941 2,271,023 Nelson Jan.'27,1942 2,312,811 Gentil Mar. 3, 1943 OTHER REFERENCES Turner, J., Institute of Metals, 1912, Vol. VII.)

pages 105-108, inclusive. a

a... A444 U Certificate of Correction Patent N 0. 2,461,280 February 8, 1949.

WILLIAM T. ISBELL It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 22, before the paragraph beginning with the words A method of removing insert I claim:;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of June, A. D. 1949.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents. 

